Analysis And Research On XDSL Spectral Compatibility

Thanks to developments in various local loop technologies and investments in digital access networks, the number of broadband subscribers has grown at an impressive pace over the last couple of years.The improvements of Digital Subscriber Line (DSL) technology enable telephone companies to optimize the utilization of their twisted-pair access networks in a flexible way, closely relating bandwidth demand and system costs. xDSL (Digital Subscriber Line) is a group of technologies for transmitting high-speed digital signals over existing metallic cables, such as EDSL(Ethernet DSL), HDSL (High-bit DSL), SDSL (Symmetric DSL), ADSL (Asymmetric DSL), RADSL (Rate Adaptive DSL), Glite ADSL, ADSL2, ADSL2+, and VDSL (Very high speed DSL), and so on. Different digital subscriber lines transmitting on loops in the same telephone cable generate crosstalk into each other. Since DSL frequencies extend into the megahertz region, crosstalk becomes the major limitation to high-speed DSL transmission Two different DSLs are spectrally compatible if they can both use the same cable with low probability of significant degradation from crosstalk. Spectrum management is the process of ensuring spectral compatibility while optimizing the loop plant. Spectrum management requires knowledge of cable plant characteristics extending into higher frequency spectra, the different DSL types, and how to compute the impact of crosstalk. Also, definitions of the level of crosstalk from one DSL type that significantly degrades another DSL type is needed, which can only reach broad acceptance through industry-wide agreements.This paper discusses the key problem of spectral compatibility in xDSL system and implements the automatic testing platform of xDSL transmission capability. The paper has the following organization. Section 2 reviews the different types of DSL, such as ISDN, HDSL, SDSL, ADSL and VDSL. It also reviews the new technology of ADSL2 and ADSL2+ in detail. Section 3 describes the twisted-pair access networks, the loop and the crosstalk,and mainly discusses the twisted-pair crosstalk. Section 4 presents the current T1.417 standard, and analyzes the necessity of the spectrum management standard in China. Section 5 provides the method of how to test the spectral compatibility and implements of automatic testing platform of ADSL transmission capability, and also draw a conclusion that the test of spectral compatibility is basically a performance test. Consequently the result demonstrate the auto-test platform of ADSL transmitting performance. Section 6 analyzes the impact of DSL spectral compatibility on introduction strategies for ADSL and VDSL, and on the other hand proves the significance of the research of spetral compatibility.